Systems and methods of monitoring operation of control rod mechanisms of nuclear power plants

ABSTRACT

Systems and methods of monitoring operation of control rod mechanisms of nuclear power plants, including obtaining signal values from existing plant test points of at least one component of a rod movement mechanism during operation of the nuclear power plant, utilizing obtained signal values to determine a present impedance of the at least one component of the rod movement mechanism during the operation of the nuclear power plant, comparing the present impedance to a reference impedance, and indicating degradation of the rod control system if the present impedance deviates from the reference impedance by a predetermined amount.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Divisional of U.S. patent application Ser. No.15/145,480, filed May 3, 2016, which is a Continuation-In-Part of U.S.application Ser. No. 13/920,631, filed on Jun. 18, 2013, U.S.application Ser. No. 13/920,649, filed on Jun. 18, 2013, and U.S.application Ser. No. 13/920,667, filed on Jun. 18, 2013, the disclosuresof which are incorporated by reference herein in their entirety.

FIELD OF INVENTION

The present application relates generally to nuclear reactor rod controlsystems, and, more particularly, relates to systems and methods ofmonitoring rod control systems of nuclear power plants to determinewhether the rod control system is operating properly.

BACKGROUND

In a nuclear Pressurized Water Reactor (PWR), the power level of thereactor is controlled by inserting and retracting control rods, whichmay include shutdown rods, in a reactor core.

Current designs of many nuclear power plants are equipped with controland shutdown rods which are inserted and withdrawn from the reactor coreto control the reactivity by absorbing neutrons. Specifically, inPressurized Water Reactors (PWRs), the movement of each rod isfacilitated by its own electromechanical magnetic jack mechanism locatedatop the reactor vessel. Two examples of rod control systems thatoperate on this principle are the Control Rod Drive Mechanism (CRDM) andControl Element Drive Mechanism (CEDM). Both of these mechanisms consistof a set of coils that provide precise vertical movement to the rod bysequentially inducing a magnetic field in the coils to operate themechanical parts of the system. The magnetic flux provides the energyneeded to hold, insert, or withdraw the rod from the reactor core.

Thus, systems and methods to verify proper rod movement and to diagnosedeveloping problems with the rod control systems would be valuable inmaintaining proper and safe operation of nuclear plants.

BRIEF SUMMARY

Example embodiments of the present general inventive concept providesystems and methods of systems and methods of monitoring rod controlsystems of nuclear power plants to determine whether the rod controlsystem is operating properly.

Additional features and embodiments of the present general inventiveconcept will be set forth in part in the description which follows and,in part, will be obvious from the description, or may be learned bypractice of the present general inventive concept.

Example embodiments of the present general inventive concept can beachieved by providing a method of monitoring a rod control system of anuclear power plant, including calculating impedance of at least onecoil of a rod movement mechanism during plant operation using anon-intrusive method for evaluation of the coil(s), comparing a measuredimpedance to a reference impedance, and determining if the measuredimpedance deviates from the reference impedance value by a predeterminedamount to indicate degradation of the rod control system.

The measuring operation can include analyzing rod control system currentand voltage signals of the at least one coil while the system is inoperation in the plant.

The measuring operation consists of non-intrusive measurements that donot hinder operations.

The measuring operation can include analyzing the impedance, consistingof resistance and inductance measurements, of any of the coils that makeup the rod control mechanism.

The measurements can determine health of coils, cables, and connectorswhich together make up the rod control mechanism.

The reference impedance can be based on a recorded impedance of the rodmovement mechanism during operation of the nuclear power plant.

Example embodiments of the present general inventive concept can also beachieved by providing a method of monitoring a rod control system of anuclear power plant, including measuring voltage and current signals ofat least one coil of a rod movement mechanism during plant operationusing a non-intrusive method for evaluation of the coil(s), calculatingan impedance of the least one coil based on measured voltage and currentsignals, recording a plurality of impedance calculations over a periodof time, and determining whether a current recorded impedance changesrelative to a prior recorded impedance by a predetermined amount toindicate degradation of the rod control system.

Example embodiments of the present general inventive concept can also beachieved by providing a system to monitor a rod control system of anuclear power plant, including an impedance determining unit todetermine an impedance of at least one coil of a rod movement mechanismduring a rod movement sequence of the rod control system, and acontroller to compare a measured impedance to a reference impedance, andto determine if the measured impedance deviates from the referenceimpedance value by a predetermined amount to indicate degradation of therod control system.

The controller can be configured to analyze current and voltagemeasurements of the at least one coil over a plurality of rod movementsequences.

Example embodiments of the present general inventive concept can also beachieved by providing a system to monitor a rod control system of anuclear power plant, including an impedance determining unit todetermine an impedance of at least one coil of a rod movement mechanismduring a rod movement sequence of the rod control system duringoperation of the nuclear power plant, and a controller to record aplurality of impedance calculations over a period of time, and todetermine whether a current recorded impedance changes relative to aprior recorded impedance by a predetermined amount to indicatedegradation of the rod control system.

Example embodiments of the present general inventive concept can also beachieved by providing a system to monitor a rod control system of anuclear power plant, including an impedance measuring unit configured toobtain signal values from existing plant test points of at least onecomponent of a rod movement mechanism during operation of the nuclearpower plant, and to utilize the obtained signal values to determine apresent impedance of the at least one component of the rod movementmechanism during the operation of the nuclear power plant, and a controlunit configured to compare the present impedance to a referenceimpedance, and to indicate degradation of the rod control system if thepresent impedance deviates from the reference impedance by apredetermined amount.

Example embodiments of the present general inventive concept can also beachieved by providing a method of monitoring a rod control system of anuclear power plant using a system an example embodiment system such asdescribed herein, the method including obtaining signal values fromexisting plant test points of at least one component of a rod movementmechanism during operation of the nuclear power plant, utilizing theobtained signal values to determine a present impedance of the at leastone component of the rod movement mechanism during the operation of thenuclear power plant, comparing the present impedance to a referenceimpedance; and indicating degradation of the rod control system if thepresent impedance deviates from the reference impedance by apredetermined amount.

Example embodiments of the present general inventive concept can also beachieved by providing a method of monitoring a rod control system of anuclear power plant, the method including establishing reference signalscorresponding to normal operation of at least one coil of a rod controlsystem during a step operation of the rod control system, the referencesignals including a plurality of reference values corresponding tovarious energy states and transitions of energy states occurring duringoperational sequences of the at least one coil, obtaining in situsignals from the at least one coil during an operational sequence of theat least one coil during operation of the nuclear power plant, the insitu signals including a plurality of in situ values corresponding tovarious energy states and transitions of energy states occurring duringpresent operational sequences of the at least one coil, comparing the insitu values to the reference values; and determining whether the in situvalues associated with a particular energy state or transition of energystates deviates from a corresponding reference value associated with theparticular energy state or transition of energy states by apredetermined amount, and, if so, associating the deviation with aparticular degradation of the rod control system.

Additional features and aspects will be apparent from the followingdetailed description, the drawings, and the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The following example embodiments are representative of exampletechniques and structures designed to carry out the objects of thepresent general inventive concept, but the present general inventiveconcept is not limited to these example embodiments. In the accompanyingdrawings and illustrations, the sizes and relative sizes, shapes, andqualities of lines, entities, and regions may be exaggerated forclarity. A wide variety of additional embodiments will be more readilyunderstood and appreciated through the following detailed description ofthe example embodiments, with reference to the accompanying drawings inwhich:

FIG. 1 illustrates a cross section of a rod control and position systemfor a pressurized water reactor according to an example embodiment ofthe present general inventive concept;

FIG. 2 illustrates a cross section of a Control Rod Drive Mechanism(CRDM) system according to an example embodiment of the present generalinventive concept;

FIG. 3 illustrates a cross section of a Control Element Drive Mechanism(CEDM) according to an example embodiment of the present generalinventive concept;

FIG. 4 is a block schematic diagram of a rod control system for a CEDMaccording to an example embodiment of the present general inventiveconcept;

FIG. 5 is a an example of CRDM currents for a withdrawal sequenceaccording to an example embodiment of the present general inventiveconcept;

FIG. 6 is a diagram of example improper moveable gripper latchingsignals according to an example embodiment of the present generalinventive concept;

FIG. 7 illustrates diagrams of example improper rod movement signalsaccording to an example embodiment of the present general inventiveconcept;

FIG. 8 illustrates diagrams of example rod movement fitting methodsaccording to an example embodiment of the present general inventiveconcept;

FIG. 9 is a diagram of an embodiment of lift coil voltage and currentduring one step of a CRDM rod movement according to an exampleembodiment of the present general inventive concept;

FIG. 10 illustrates an equivalent electrical circuit of a CRDM coilaccording to an example embodiment of the present general inventiveconcept;

FIG. 11 illustrates a block diagram of a data driven step counter systemaccording to an example embodiment of the present general inventiveconcept; and

FIG. 12 illustrates a timing diagram of an embodiment of CRDM currentsignals for an insertion and withdrawal sequence according to an exampleembodiment of the present general inventive concept.

DETAILED DESCRIPTION

Reference will now be made to various example embodiments of the presentgeneral inventive concept, examples of which are illustrated in theaccompanying drawings and illustrations. The example embodiments aredescribed herein in order to explain the present general inventiveconcept by referring to the figures.

The following detailed description is provided to assist the reader ingaining a comprehensive understanding of the methods, apparatuses,and/or systems described herein. Accordingly, various changes,modifications, and equivalents of the methods, apparatuses, and/orsystems described herein will be suggested to those of ordinary skill inthe art. The described progression of processing operations describedare merely examples, however, and the sequence of operations is notlimited to that set forth herein and may be changed as is known in theart, with the exception of operations necessarily occurring in a certainorder. Also, description of well-known functions and constructions maybe omitted for increased clarity and conciseness.

Note that spatially relative terms, such as “up,” “down,” “right,”“left,” “beneath,” “below,” “lower,” “above,” “upper” and the like, maybe used herein for ease of description to describe one element orfeature's relationship to another element(s) or feature(s) asillustrated in the figures. Spatially relative terms are intended toencompass different orientations of the device in use or operation inaddition to the orientation illustrated in the figures. For example, ifthe device in the figures is turned over or rotated, elements describedas “below” or “beneath” other elements or features would then beoriented “above” the other elements or features. Thus, the exemplaryterm “below” can encompass both an orientation of above and below. Thedevice may be otherwise oriented (rotated 90 degrees or at otherorientations) and the spatially relative descriptors used hereininterpreted accordingly.

Various example embodiments of the present general inventive conceptsprovide systems and methods improve the versatility, practicality, andefficiency of control rod systems in nuclear power plants. For example,embodiments of the present general inventive concept can be configuredto monitor operation of rod control systems to verify proper movement ofcontrol rods in nuclear power plants. Example embodiments have beendeveloped to aid in verifying proper rod movement from the coil currenttraces, due to increasing occurrences of slipped and stuck rodsthroughout the nuclear industry. As another example, embodiments of thepresent general inventive concept have been developed to determine,during normal plant operation, impedance measurements that can be usedto verify proper operation of the coils, cables, and connectors thatmake up the rod control mechanism. Detected changes in impedance can beused to detect degradation and aging. As another example, embodiments ofthe present general inventive concept provide systems and methods toconfirm rod movement, determine step movements, and provide stepindication of control rods in nuclear power plants. While existingmethods make count steps based on demands from the control room,embodiments of the present general inventive concept make an assessmentof rod movement from the output of the rod movement mechanism. Thisallows steps to only be counted when movement actually occurs based onverification of a proper rod movement sequence. Such a method will helpmitigate step count errors which can cause reactor trips.

FIG. 1 illustrates a cross section of a rod position control system 15for a Pressurized Water Reactor according to an example embodiment ofthe present general inventive concept. Referring to FIG. 1, the powerlevel of the reactor 10 is controlled by inserting and retractingcontrol rods 12 (which may include the shutdown rods) into the reactorcore 14 to control the reactivity by absorbing neutrons. Movement ofeach rod may be facilitated by its own electromechanical magnetic jackmechanism located atop a reactor vessel referred to as a rod controlsystem, or rod position control system 15.

In the embodiment of FIG. 1, the control rods are moved by a Control RodDrive Mechanism (CRDM) which uses electromechanical jacks to raise orlower the control rods in increments. The CRDM may include a lift coil,a moveable coil, and a stationary coil controlled by a Rod ControlSystem (RCS), and a ferromagnetic drive rod coupled to the control rodto move within a pressure housing 16. The drive rod may include a numberof circumferential grooves at single step intervals (“steps”) thatdefine a range of movement for the control rod. An example step intervalmay be ⅝ inch. An example drive rod may contain approximately 231 steps,or grooves, which may vary. A moveable gripper mechanically engages thegrooves of a drive rod when its coil is energized, and disengages fromthe drive rod when the coil is de-energized. Energizing a lift coilraises the moveable gripper and the associated control rod if themoveable coil is energized by one step. Energizing the moveable coil andde-energizing the lift coil moves the control rod down one step.Similarly, when energized, a stationary gripper engages the drive rod tomaintain the position of the control rod and, when de-energized,disengages from the drive rod to allow the control rod to move. Aconventional system may include two coil stacks for each control rod andthe associated componentry for processing the signals from the coilstacks. Each coil stack may be an independent channel of coils placedover the pressure housing. Each channel typically includes 21 coils, andthe coils may be interleaved and positioned at approximately 3.75 inchintervals (6 steps). The coil stack assembly includes a set of coilsthat generate magnetic flux. For example, the coil stack assembly canprovide magnetic energy for a latch assembly. It surrounds the latchhousing and includes three coils that operate corresponding magnets inthe latch assembly. Nickel-plated cast iron components may provide thesupport structure for the coils and conduct magnetic flux to the latchassembly. Electrical connectors may be sealed against moisture and dustand are easily coupled and uncoupled. The coils receive electricalimpulses from a system such as a CRDM control system and are cooledexternally by forced air. The latch assembly converts the magneticenergy into linear motion. A drive rod assembly connects a CRDM motor toa control rod. A pressure housing retains the reactor coolant andsupports other components of the CRDM.

The RCS may include a logic cabinet and a power cabinet, which aredescribed in more detail herein. The logic cabinet may receive manualdemand signals from an operator or automatic demand signals from areactor control and provides command signals needed to operate shutdownand control rods according to a predetermined schedule. The powercabinet provides a programmed current. The rod movement demand,generated by either the operator or the reactor control system, isreceived and processed by the cabinet logic. The logic cabinet thencontrols the power switching circuitry that is responsible for themotion of the rod control mechanism. There are currently three differentpower levels that the switching circuitry provides to the drivemechanism. These power levels include the ‘High’ state, which is used toquickly energize the coil, ‘Reduced’, which is used to maintain theenergized state, and ‘Low’, which is used for the coil in the off state.The logic cabinet is responsible for providing the sequence at whichthese power levels should be applied to the coils for the desired rodmovement.

FIG. 2 illustrates a cross section of a Control Rod Drive Mechanism(CRDM) system according to an example embodiment of the present generalinventive concept. As illustrated in FIG. 2, an example CRDM system 200includes three electric coils (Lift Coil 224, Movable Coil 228, andStationary Coil 236) and two electromagnetic jacks with grippers(Movable Gripper 232 and Stationary Gripper 240). A connector 250 andcable 252 are illustrated to indicate possible test points for systemanalysis to check signal levels associated with the coils, but for thesake of clarity only one such connector and cable are illustrated. It isunderstood that such cables and connectors may be found at numerouslocations and associated with various components in this and similarsystems. The drive rod 242 is grooved which allows the grippers toengage and support the weight of the drive rod 242. These grooves allowthe mechanism to insert and withdraw the rod in ⅝″ steps. The moveablegripper 232 mechanically engages the grooves of the drive rod 242 whenits coil is energized, and disengages from the drive rod 242 when thecoil is de-energized. Energizing the lift coil 224 raises the moveablegripper 232 and the associated control rod if the moveable coil 228 isenergized by one step. Energizing the moveable coil 228 andde-energizing the lift coil 224 moves the control rod down one step.Similarly, when energized, the stationary gripper 240 engages the driverod 242 to maintain the position of the control rod and, whende-energized, disengages from the drive rod 242 to allow the control rodto move.

FIG. 3 illustrates a cross section of a Control Element Drive Mechanism(CEDM) system according to an example embodiment of the present generalinventive concept. As illustrated in FIG. 3, an example CEDM system 300includes five electric coils (Lift Coil 324, Upper Gripper Coil 328,Pulldown Coil 332, Load Transfer Coil 336, and Lower Gripper Coil 340)and two electromagnetic jacks with grippers (Upper Gripper 350 and LowerGripper 354). The drive rod for this system is grooved to allow the rodto insert or withdraw from the reactor core in single step increments,for example, ¾″ steps, when the coils are energized in a particularsequence. The sequencing is established by the logic cabinet through aset of current orders which are provided to the power cabinet firing andregulation cards for low, reduced, or full levels of current to beapplied to the coils.

FIG. 4 is a block schematic diagram of a rod control system for a CEDMaccording to an example embodiment of the present general inventiveconcept. It is noted that while FIG. 4 illustrates a CEDM system, manyof the elements and procedures will be the same or similar to a CRDM orother similar system. For example, although an example connector 250 andcable 252 are illustrated for the lift coil 224 of the CRDM systemillustrated in FIG. 2, it is understood that such elements are alsopresent in the CEDM system of FIG. 3. Referring to FIG. 4, an examplerod control system includes controls and indicators in the main controlroom, control logic cabinets, power switching cabinets, powerdistribution from the motor generator sets, and the rod controlmechanism itself. FIG. 4 also illustrates a system to monitor the rodcontrol system of a nuclear power plant, the system 400 configured suchthat a user may measure impedance of at least one coil of the rodcontrol system during operation of the nuclear power plant during normaloperation, so that diagnostic evaluations may be made without intrusiveefforts such as shutting down the plant or CRDM system. The system 400may include an impedance measuring unit 410 to measure impedance of acoil, or associated cables or connectors, at existing site test pointswithout interrupting service, and a control unit 420 to compare themeasured impedance value to an associated reference impedance value andto determine if the measured impedance value deviates from the referenceimpedance value. The impedance measuring unit 410 may be configured toobtain voltage and/or resistance values of at least one of a coil,cable, and a connector of the rod control system, and use these obtainedvalued to determine the impedance of the component. Thus, the impedancemeasuring unit 410 may measure impedance by using obtained voltageand/or current measurements to determine the impedance. The measurementscan determine health of coils, cables, and connectors which togethermake up the rod control mechanism. Deviation from the reference value bya predetermined amount may indicate degradation of the rod controlsystem. The control unit 420 may be configured to analyze current andvoltage measurements of the coil or associated component. The referenceimpedance value may be based on historical impedance measurements of therod movement mechanism during operation of the nuclear power plant. Thesystem 400 may include a recording unit 440 to record a plurality ofimpedance calculations obtained over time during operation of the powerplant. The control unit 420 may compare a current calculated impedancevalue with the prior recorded impedance value to determine if there is adeviation that indicates a problem with the rod control system. Changesin impedance can indicate degradation and aging of thecomponents/system. The system 400 may be provided with a user interface450 to allow a user to interact with the system in order to, forexample, identify coils or other components to be tested, and agraphical output 430 may be provided to display values such as componentidentification, graphical signal responses, etc. For example, thegraphical output 430 may display measured voltage and current valuesassociated with a lift coil over at least one step of a cycle such as alift movement cycle, in which the rod is lifted by a step. Exampleembodiments of the system may also include a diagnostic step counter 460to count steps corresponding to measure values, the counting of thesteps being comparable to the count kept by the existing plant stepcounter. According to various example embodiments of the present generalinventive concept, more or less components may be included in the system400, which may be handheld for ease of movement to different stations inthe nuclear power plant. Taking into consideration heat resistanceproperties of the coil such as coil material, coil length, coilthickness, number of wraps of coil, heat capacity of material, etc., theimpedance values and/or current/voltage values measured over time can beused by the control unit to determine coil temperature. For example, insome embodiments, it is possible to determine that lower resistancevalues measured over time can result in the coil heating to a highertemperature faster.

FIG. 5 is an example of CRDM currents for a withdrawal sequenceaccording to an example embodiment of the present general inventiveconcept. As illustrated in FIG. 5, the coil current data embodiesinformation that can be used to determine proper rod movement andoperation. For example, the latching of the stationary and moveablegripper can be confirmed in the coil current data. A rod latchingproblem could result in a rod slipping or dropping causing the stepcount in the control room to become unreliable.

The current diagram 600 shows a normal current 610 trace when the rod iswithdrawn from a reactor vessel as requested from control signalsassociated with a withdrawal sequence. Referring to FIG. 5, during aStage 1, a Stationary Gripper (SG) coil is energized to a reducedcurrent, wherein the SG is the only gripper supporting the rod shaft. Ina Stage 2, the SG coil is energized to full, while a Moveable Gripper(MG) coil energizes and latches to the rod shaft. In a Stage 3, the SGcoil discharges to an inactive state so that the rod load is transferredcompletely to the MG. In a Stage 4, the Lift Coil (LC) is energized tofull until the rod shaft is lifted a predetermined amount. In a Stage 5,the LC is reduced until the SG coil energizes and latches the gripperagain. In a Stage 6, once the SG is latched, the LC and MG disengage,the SG coil discharges to reduced current and the CRDM is returned toStage 1.

FIG. 6 is a diagram of example improper moveable gripper latchingsignals according to an example embodiment of the present generalinventive concept. As illustrated in FIG. 6, in addition to timing andsequencing, the coil current data holds much more information concerningproper rod movement and operation, and the latching of the stationaryand moveable gripper can be confirmed in the coil current data. This isimportant as a latching problem could result in a rod slipping ordropping causing the step count in the control room to becomeunreliable.

FIG. 7 illustrates diagrams of example improper rod movement signalsaccording to an example embodiment of the present general inventiveconcept. As illustrated in FIG. 7, a rod has become temporarilyimmovable. In this figure, two stationary coil traces collected on thesame rod are shown. The trace 814 shows the stuck rod and the\ trace 810shows the rod right after the problem was resolved. To help diagnosethis problem, and any other issues with CRDM loading, example methodswere developed to determine proper rod movement, examples of which areillustrated in FIG. 8.

FIG. 8 illustrates diagrams of example rod movement fitting methodsaccording to an example embodiment of the present general inventiveconcept. An example method 830 applies a simple exponential fit to thecurrent traces and calculates a response metric of the CRDM to the rodmovement request. Another method 840 applies a linear fit to the rise ofthe current trace, and the slope is used as an indication of proper rodmovement. Another method 850 calculates the integral of the current fromthe time the current goes high until it returns to the low or reducedstate. These example methods produced a useful metric for determiningrod movement problems, and the results were very accurate from step tostep with a significant change noticed when a problem did exist. Otherknown or later developed methods could also be implemented withoutdeparting from the broader scope and spirit of the present generalinventive concept.

Example systems and methods of the present general inventive concept canbe used to make non-intrusive impedance measurements on rod controlsystem coils in-situ. Coil signal measurements such as coil voltage andcoil current can be acquired from existing plant test points.

FIG. 9 illustrates an example graph 870 of measured voltage and currentapplied to a lift coil over time during one step of a CRDM movementcycle according to an example embodiment of the present generalinventive concept. The relationship of measured voltage and current overtime may be utilized to determine coil and cable health. A change inthese values may be an indication of a rod movement failure, electricaldegradation, or mechanical degradation. Voltage and current measurementsmay be used in determining coil and cable health in a non-intrusiveimpedance measurement on the CRDM coils.

FIG. 10 provides an example equivalent electrical circuit 920 of a CRDMcoil embodiment according to an example embodiment of the presentgeneral inventive concept. This circuit allows the resistance andinductive portions of the coil to be calculated.

If the current Ian in the coil is at steady state, the inductance L inthe coil can be treated as a short, resulting in a purely resistive coilR. This leaves the resistance of the coil R to be calculated by Ohm'slaw as shown by Equation 928.

R=V _(REG) /I _(COIL)  (Equation 928)

Using the resistance value from equation 928, the inductance L inEquation 932 can be solved accordingly.

$\begin{matrix}{V_{REG} = {\frac{d({LI})}{dt} + {RI}}} & \left( {{Equation}\mspace{14mu} 932} \right)\end{matrix}$

The amount work (W) delivered to a coil over a period of time can becalculated using equation 922 illustrated in FIG. 10. In an example, thework can be calculated over a rod movement sequence to detect changes inthe amount of energy needed to move the rod. The examples describedherein provide a metric which may be utilized to diagnose rod movementproblems because the calculation results may be predictable from step tostep wherein a significant variation from normal may be noticed becauseone or more problems such as, for example, improper rod movement, rodmovement failure, electrical degradation, mechanical degradation, etc.,exists. Changes in the level of work, and/or changes in impedance andrelated values, can detect problems with the mechanism.

Presently, step counters that are used to display the current step ofthe drive mechanism are based on up or down rod movement commands comingfrom either the reactor operator or reactor control system. Since thestep counter is based on demanded movement, and not actual movement, theinformation may become inaccurate if a problem occurs in the drivemechanism or rod control system. An example solution is with a datadriven solution that uses the outputs of the drive mechanism coils toconfirm rod movement and determine the step of the rod.

FIG. 11 illustrates a block diagram of a data driven step counter systemaccording to an example embodiment of the present general inventiveconcept. In this embodiment, the data driven step counter appliesadvanced analysis techniques to signals acquired from existing planttest points so that no additional sensors are required to confirm theactual movement of the rod. The counter is configured to detect thebeginning of a new rod movement event. The raw data from drive mechanismcan then be processed 952 to prepare it for step analysis 954. In someembodiments, the step analysis determines the direction of the step,validates the sequencing, verifies that the latches have properlyengaged, and confirms that the LC properly lifts its responsible gripperassembly. If the step analysis concludes that an insert or withdrawmovement has actually occurred, the step counter will be decremented orincremented respectively. If the step analysis detects an error with thesequence, latching, or movement of the rod, the step counter can remainon its current step and a warning can be provided. The step counterstores the current step and sends the step information to the stepdisplay 958. The step display provides step indication for all drivemechanisms.

FIG. 12 illustrates a timing diagram of an embodiment of CRDM currentsignals for an insertion and withdrawal sequence according to an exampleembodiment of the present general inventive concept. Example embodimentsof the data driven step counter can determine the direction of the stepbased on the initial condition of the step. For example, with the CRDMsystem as illustrated in FIG. 7, steps start with the SG going ‘High’970 and the direction can be determined based on the states of the othertwo coils. If the MG engages prior to the LC going high, the step can bedetermined to be a withdrawal. If the LC is energized high 974 beforethe MG engages, the step can be determined to be an insertion. Thus, thestep direction can be determined from the coil output data.

Referring to FIG. 12, the counter can be configured to verify that thesequence for the demanded direction was correct before the step can beconsidered. Using a CRDM as an example, if the LC engages too lateduring an insertion sequence it could actually cause the rod to move inthe wrong direction. Therefore, in some embodiments, the data from thecoil outputs can be used to verify the sequence of the ‘High’,‘Reduced’, and ‘Low’ states from each of the coils and, consequently, todetermine if a step could have occurred. The CEDM and CRDM rod controlsystems consist of different components and both utilize a particularsequence of events in order to move the rod in the demanded direction.However, the methods are not limited to the sequences described in thisexample. For example, some plants have implemented a double grippermodification for the CRDM which allows both the MG and SG to support theweight of the rod during a hold state. Although such modifications maychange the sequence of events used by the CRDM to complete a step, theexample systems and methods of the present general inventive concept canstill be applied for considering the rod movement.

In some embodiments, verifying the sequencing of the coil states alonemay not be enough to verify that a step of the drive rod has occurred.For example, the latching of the magnetic jacks may be confirmed as wellas the times at which the latches occur. Moreover, the coil(s)associated with a given gripper may go to a high state but that does notguarantee that the latch was properly engaged. To verify the latchengagement, embodiments of the present general inventive concept examinethe phenomena which causes the latch ‘dip’ in the coil output data. Thatis, when a gripper coil has enough energy it causes the gripper assemblyto be slightly lifted causing the gripper to engage the grooved rod. Theupward movement of the gripper causes a back EMF to be induced in thecoil which causes the latch ‘dip’ seen on the coil current data. Forexample, if the lift coil cannot perform the lift movement over thedistance required to complete one step the rod will most likely remainon the current step. Additionally, if the rod becomes stuck, LC onlypartially lifts the gripper assembly, or some other obstacle hinders thegrippers to fully engage or disengage it will be detected in the grippermovement analysis. Further analysis of this change in current can verifythat the grippers have been fully engaged or disengaged, and that thelift coils have properly lifted the gripper assembly for which they areresponsible. The time at which the latch has been engaged should also becompared to other critical events in the coil sequence. For instance, ifthe MG disengages prior to the SG engaging in the step of the CRDM, thenthe rod may slip or completely be dropped into the reactor core.

An example embodiment of the present general inventive concept mayprovide a method of monitoring a rod control system of a nuclear powerplant including measuring an input to and/or output signal from at leastone coil of a rod movement mechanism at one or more predetermined timesrelative to an initial energizing of a mechanism coil, calculating asignal parameter from the measured signal and comparing the measuredsignal to a reference signal parameter; and determining if thecalculated parameter deviates from the reference signal parameter by apredetermined amount to indicate impairment of the rod control system.In example embodiments, the reference signal parameter may be based onat least one of the following: an ideal exponential curve; an ideallinear curve; the integral of a reference signal curve over apredetermined time interval and a work calculation from a reference rodmovement mechanism input and output

An example embodiment of the present general inventive concept mayprovide a system to monitor rod movement signals of a rod control systemof a nuclear power plant including a system to measure one or moresignals applied to at least one coil of a rod movement mechanism, and acontroller to acquire a measured signal at one or more predeterminedtimes relative to energizing of a mechanism coil, to compare themeasured signal to a reference signal parameter, and to determine if themeasured signal deviates from the reference signal parameter by apredetermined amount to indicate impairment of the rod control system.An example system may further include an output unit to output a signalwhen the measured signal deviates from the reference signal parameter byone or more predetermined amounts. In example embodiments, the referencesignal parameter may be based on at least one of the following: an idealexponential curve; an ideal linear curve; a work calculation from thereference rod movement mechanism input and output and the integral of areference signal curve over a predetermined time interval.

An example embodiment of the present general inventive concept mayprovide a method of monitoring a rod control system of a nuclear powerplant including calculating an impedance of at least one coil of a rodmovement mechanism using a non-intrusive method that utilizes existingplant signals, thereby allowing impedance to be calculated in-situ whilethe rod control system is online. In example embodiments, thecalculating may include comparing a measured impedance to a referenceimpedance, and determining if the measured impedance deviates from thereference impedance value by a predetermined amount to indicatedegradations or failures of the rod control system. In exampleembodiments, the calculating may include analyzing current and voltagesignals. In example embodiments, the calculating may include measuring aresistance of at least one of the following: a coil, a cable, and atleast one connector and wherein a measured resistance is used todetermine the coil temperature of a rod movement mechanism above areactor core. In example embodiments, the calculating may includemeasuring an inductance of at least one of the following: a coil, acable, and at least one connector. In example embodiments, thecalculating may include analyzing the impedance of at least one coil. Anexample reference impedance may be based on historical impedancecalculations of the at least one coil.

An example embodiment of the present general inventive concept mayprovide a method of monitoring a rod control system of a nuclear powerplant including measuring voltage and current signals of at least onecoil of a rod movement mechanism while the system is in operation in theplant, recording a plurality of impedance calculations over a period oftime, calculating an impedance of the least one coil based on themeasured voltage and current signals, and determining whether a currentrecorded impedance changes relative to a prior recorded impedance by apredetermined amount indicate degradation of the rod control system.

An example embodiment of the present general inventive concept mayprovide a system to monitor a rod control system of a nuclear powerplant including an impedance measuring unit to measure an impedance ofat least one coil of a rod movement mechanism during plant operationusing a non-intrusive method for evaluation of the at least one coil,and a controller to compare a measured impedance to a referenceimpedance, and to determine if the measured impedance deviates from thereference impedance value by a predetermined amount to indicatedegradation of the rod control system. An example controller may beconfigured to analyze current and voltage measurements of the at leastone coil. In example embodiments, the reference impedance may be basedon historical impedance measurements of the rod movement mechanismduring operation of the nuclear power plant.

An example embodiment of the present general inventive concept mayprovide a system to monitor a rod control system of a nuclear powerplant including an impedance determining unit to determine an impedanceof at least one coil of a rod movement mechanism during plant operationusing a non-intrusive method for evaluation of the at least one coil,and a controller to record a plurality of impedance calculations over aperiod of time, and to determine whether a current recorded impedancechanges relative to a prior recorded impedance by a predetermined amountto indicate degradation of the rod control system.

An example embodiment of the present general inventive concept mayprovide a system to monitor a rod control system of a nuclear powerplant, including an impedance measuring unit to measure an impedance ofat least one coil of a rod movement mechanism during operation of thenuclear power plant operation using a non-intrusive method forevaluation of the at least one coil, and a controller to compare ameasured impedance value to a reference impedance value, and todetermine if the measured impedance value deviates from the referenceimpedance value by a predetermined amount to indicate degradation of therod control system. The controller may be configured to analyze currentand voltage measurements of the at least one coil. The referenceimpedance value may be based on historical impedance measurements of therod movement mechanism during operation of the nuclear power plant.

An example embodiment of the present general inventive concept mayprovide a system to monitor a rod control system of a nuclear powerplant, including an impedance measuring unit to calculate impedancevalues of the rod control system in situ during operation of the powerplant, a recording unit configured to record a plurality of impedancecalculations obtained over time during operation of the power plant, anda control unit configured to compare a current calculated impedancevalue with a prior recorded impedance value, and to determine if thecurrent calculated impedance value deviates from the prior recordedimpedance value by a predetermined amount to identify a problem with therod control system. The impedance measuring unit may be configured tomeasure voltage and current values delivered to a lift coil of the rodcontrol system over time, and the control unit may be configured tocalculate an amount of work (W) delivered to the coil based on measuredvoltage and current values delivered to the lift coil over time, whereinthe recording unit may be configured to store a plurality of work valuesdelivered to the lift coil over time, and the control unit may beconfigured to compare a current work value to a prior work value todetermine if the current work value deviates from the prior work valueby a predetermined amount to detect changes in the amount of energy usedto move a control rod. The impedance measuring unit may be configured toobtain voltage and resistance values of at least one of a lift coil, acable, and a connector of the rod control system. The controller may beconfigured to determine a lift coil temperature based on an obtainedresistance value. The system may further include a graphical output todisplay measured voltage and current values delivered to a lift coilover at least one step of a lift movement cycle.

An example embodiment of the present general inventive concept mayprovide a system to monitor a rod control system of a nuclear powerplant, including an impedance measuring unit configured to obtain signalvalues from existing plant test points of at least one component of arod movement mechanism during operation of the nuclear power plant, andto utilize the obtained signal values to determine a present impedanceof the at least one component of the rod movement mechanism during theoperation of the nuclear power plant, and a control unit configured tocompare the present impedance to a reference impedance, and to indicatedegradation of the rod control system if the present impedance deviatesfrom the reference impedance by a predetermined amount. The impedancemeasuring unit may obtain voltage and current values as the signalvalues. The at least one component of the rod movement mechanism mayinclude a coil, connector, cable, or any combination thereof in the rodmovement mechanism. The reference impedance may correspond to historicalimpedance measurements of the rod movement mechanism during operation ofthe nuclear power plant. The system may further include a recording unitconfigured to record one or more determined impedances corresponding tothe at least one component to determine the reference impedance. Theimpedance measuring unit may be further configured to measure aresistance of the at least one component to determine a temperature ofthe at least one component. The system may further include a graphicaloutput configured to display one or more signal values associated withthe at least one component. The display may include plotting the one ormore signal values over a time period including one or more energystates and transitions between energy states of the at least onecomponent. The present impedance may be recorded over a length of timeincluding one or more energy states and transitions between energystates of the at least one component, the energy states including afully energized state, a reduced state, an inactive state, or anycombination thereof.

An example embodiment of the present general inventive concept mayprovide a method of monitoring a rod control system of a nuclear powerplant using an example embodiment system such as described herein, themethod including obtaining signal values from existing plant test pointsof at least one component of a rod movement mechanism during operationof the nuclear power plant, utilizing the obtained signal values todetermine a present impedance of the at least one component of the rodmovement mechanism during the operation of the nuclear power plant,comparing the present impedance to a reference impedance, and indicatingdegradation of the rod control system if the present impedance deviatesfrom the reference impedance by a predetermined amount. The obtainedsignal values may be voltage and current values. The at least onecomponent of the rod movement mechanism may include a coil, connector,cable, or any combination thereof in the rod movement mechanism. Thereference impedance may correspond to historical impedance measurementsof the rod movement mechanism during operation of the nuclear powerplant. The method may further include recording one or more determinedimpedances corresponding to the at least one component to determine thereference impedance. The method may further include measuring aresistance of the at least one component to determine a temperature ofthe at least one component. The method may further include displayingone or more signal values associated with the at least one component ona graphical display. The displaying may include plotting the one or moresignal values over a time period including one or more energy states andtransitions between energy states of the at least one component. Thepresent impedance may be recorded over a length of time including one ormore energy states and transitions between energy states of the at leastone component. The energy states of the at least one component mayinclude a fully energized state, a reduced state, an inactive state, orany combination thereof. The determining, comparing, and indicatingoperations may be performed on a lift coil, moveable gripper coil, andstationary gripper coil during six stages of a rod withdrawal sequence,including: a first stage in which the stationary gripper coil isenergized at a reduced state, and a stationary gripper is solely latchedto the rod; a second stage in which the stationary gripper coil isenergized to a fully energized state, and the moveable gripper coil isenergized to the fully energized state to latch a moveable gripper tothe rod; a third stage in which the stationary gripper coil isdischarged to an inactive state such that the movable gripper is solelylatched to the rod; a fourth stage in which the lift coil is energizedto the fully energized stage until the rod is lifted a predetermineddistance; a fifth stage in which the lift coil is discharged to thereduced state until the stationary grip coil is energized to the fullyenergized state to latch the stationary grip to the rod; and a sixthstage in which the lift coil and moveable gripper coil are discharged tothe inactive state, and the stationary grip coil is discharged to thereduced state.

An example embodiment of the present general inventive concept mayprovide a method of monitoring a rod control system of a nuclear powerplant, the method including establishing reference signals correspondingto normal operation of at least one coil of a rod control system duringa step operation of the rod control system, the reference signalsincluding a plurality of reference values corresponding to variousenergy states and transitions of energy states occurring duringoperational sequences of the at least one coil, obtaining in situsignals from the at least one coil during an operational sequence of theat least one coil during operation of the nuclear power plant, the insitu signals including a plurality of in situ values corresponding tovarious energy states and transitions of energy states occurring duringpresent operational sequences of the at least one coil, comparing the insitu values to the reference values, and determining whether the in situvalues associated with a particular energy state or transition of energystates deviates from a corresponding reference value associated with theparticular energy state or transition of energy states by apredetermined amount, and, if so, associating the deviation with aparticular degradation of the rod control system. Such a method may beperformed by an example system configured according to an exampleembodiment of the present general inventive concept. The at least onecoil may include a lift coil, a movable coil, a stationary coil, anupper gripper coil, a pulldown coil, a load transfer coil, a lowergripper coil, or any combination thereof, wherein each coil has its ownrespective operational sequence including various respective energystates and transitions of energy states occurring during operationsequences of each respective coil, wherein the reference values and insitu values include a plurality of values corresponding to the variousrespective energy states and transitions of energy states, and whereinthe determining operation includes determining whether the in situvalues associated with any one or more of the respective energy statesor transitions of energy states deviates from a corresponding referencevalue associated with the particular respective energy state ortransition of energy state.

An example embodiment of the present general inventive concept mayprovide a method of monitoring step movements of control rods of anuclear power plant including measuring output signals of a plurality ofrod movement coils during a step movement sequence of one or morecontrol rods, analyzing the output signals to verify the rod movement,and analyzing the output signals to determine a direction of the stepmovement sequence. An example method may further include verifying stepmovement sequence. An example method may further include verification ofmechanical movement of the mechanism as it relates to the rod stepmovement sequence. An example method may further include decrementing orincrementing a step counter based on the analyzing and comparingoperations. An example method may further include generating a warningsignal if a determined direction of step movement does not correspond toa commanded direction of step movement and/or if a difference betweenthe one or more output signals deviates from the reference signal by apredetermined amount. An example method may further include displayingstep information.

An example embodiment of the present general inventive concept mayprovide a step counter system for a rod control system of a nuclearpower plant including a measuring unit to measure output signals of aplurality of rod movement coils during a step movement sequence of oneor more control rods, and a controller to analyze the output signals todetermine a direction of the step movement sequence, analyzing theoutput signals to verify the rod movement. In example embodiments, thecontroller may be configured to decrement or increment a step counterbased on a determined direction of the step movement sequence and acomparison to one or more output signals of the reference output signal.In example embodiments, the controller may be configured to generate awarning signal if a determined direction of step movement does notcorrespond to a commanded direction of step movement and/or if adifference between the one or more output signals deviates from thereference sequence by a predetermined amount. An example system mayfurther include a display unit to display step counter information baseda determined direction of the step movement sequence and verificationthrough a comparison of the one or more output signals to the referencerod movement sequence.

The examples described herein provide a metric which may be utilized todiagnose rod movement problems because the calculation results may bepredictable from step to step wherein a significant variation fromnormal may be noticed because of one or more problems, such as improperrod movement, rod movement failure, electrical degradation, mechanicaldegradation, etc., exists. Changes in the level of work, and/or changesin impedance and related values, can detect problems with the mechanism.

It is noted that the simplified diagrams and drawings do not illustrateall the various connections and assemblies of the various components,however, those skilled in the art will understand how to implement suchconnections and assemblies, based on the illustrated components,figures, and descriptions provided herein, using sound engineeringjudgment.

Numerous variations, modifications, and additional embodiments arepossible, and accordingly, all such variations, modifications, andembodiments are to be regarded as being within the spirit and scope ofthe present general inventive concept. For example, regardless of thecontent of any portion of this application, unless clearly specified tothe contrary, there is no requirement for the inclusion in any claimherein or of any application claiming priority hereto of any particulardescribed or illustrated activity or element, any particular sequence ofsuch activities, or any particular interrelationship of such elements.Moreover, any activity can be repeated, any activity can be performed bymultiple entities, and/or any element can be duplicated.

While the present general inventive concept has been illustrated bydescription of several example embodiments, it is not the intention ofthe applicant to restrict or in any way limit the scope of the inventiveconcept to such descriptions and illustrations. Instead, thedescriptions, drawings, and claims herein are to be regarded asillustrative in nature, and not as restrictive, and additionalembodiments will readily appear to those skilled in the art upon readingthe above description and drawings.

What is claimed is:
 1. A method of monitoring operation of a control rodmovement mechanism of a nuclear power plant, comprising: obtainingsignal values from existing plant test points of at least one componentof the control rod movement mechanism during operation of the nuclearpower plant; utilizing obtained signal values to determine a presentimpedance of the at least one component during operation of the nuclearpower plant; comparing the present impedance to a reference impedance;and indicating degradation of the at least one component if the presentimpedance deviates from the reference impedance by a predeterminedamount.
 2. The method of claim 1, wherein the present impedance isrecorded over a length of time including one or more energy states andtransitions between energy states of the at least one component, theenergy states including a fully energized state, a reduced state, aninactive state, or any combination thereof.
 3. The method of claim 1,wherein the obtained signal values are voltage and current values. 4.The method of claim 1, wherein the at least one component includes acoil, connector, cable, or any combination thereof in the rod movementmechanism.
 5. The method of claim 1, wherein the reference impedancecorresponds to historical impedance measurements of the control rodmovement mechanism during operation of the nuclear power plant.
 6. Themethod of claim 1, further comprising recording one or more determinedimpedances corresponding to the at least one component to determine thereference impedance.
 7. The method of claim 1, further comprisingmeasuring a resistance of the at least one component to determine atemperature of the at least one component.
 8. The method of claim 1,further comprising displaying one or more signal values associated withthe at least one component on a graphical display.
 9. The method ofclaim 8, wherein the displaying includes plotting the one or more signalvalues over a time period including one or more energy states andtransitions between energy states of the at least one component.
 10. Themethod of claim 1, wherein the present impedance is recorded over alength of time including one or more energy states and transitionsbetween energy states of the at least one component.
 11. The method ofclaim 10, wherein the energy states of the at least one componentincludes a fully energized state, a reduced state, an inactive state, orany combination thereof.
 12. The method of claim 1, wherein thedetermining, comparing, and indicating operations are performed on alift coil, moveable gripper coil, and stationary gripper coil during sixstages of a rod withdrawal sequence, including: a first stage in whichthe stationary gripper coil is energized at a reduced state, and astationary gripper is solely latched to the rod; a second stage in whichthe stationary gripper coil is energized to a fully energized state, andthe moveable gripper coil is energized to the fully energized state tolatch a moveable gripper to the rod; a third stage in which thestationary gripper coil is discharged to an inactive state such that themovable gripper is solely latched to the rod; a fourth stage in whichthe lift coil is energized to the fully energized stage until the rod islifted a predetermined distance; a fifth stage in which the lift coil isdischarged to the reduced state until the stationary grip coil isenergized to the fully energized state to latch the stationary grip tothe rod; and a sixth stage in which the lift coil and moveable grippercoil are discharged to the inactive state, and the stationary grip coilis discharged to the reduced state.
 13. A method of monitoring a rodcontrol system of a nuclear power plant, the method comprising:establishing reference signals corresponding to normal operation of atleast one coil of a rod control system during a step operation of therod control system, the reference signals including a plurality ofreference values corresponding to various energy states and transitionsof energy states occurring during operational sequences of the at leastone coil; obtaining in situ signals from the at least one coil during anoperational sequence of the at least one coil during operation of thenuclear power plant, the in situ signals including a plurality of insitu values corresponding to various energy states and transitions ofenergy states occurring during present operational sequences of the atleast one coil; comparing the in situ values to the reference values;and determining whether the in situ values associated with a particularenergy state or transition of energy states deviates from acorresponding reference value associated with the particular energystate or transition of energy states by a predetermined amount, and, ifso, associating the deviation with a particular degradation of the rodcontrol system.
 14. The method of claim 13, wherein the at least onecoil includes a lift coil, a movable coil, a stationary coil, an uppergripper coil, a pulldown coil, a load transfer coil, a lower grippercoil, or any combination thereof, wherein each coil has its ownrespective operational sequence including various respective energystates and transitions of energy states occurring during operationsequences of each respective coil, wherein the reference values and insitu values include a plurality of values corresponding to the variousrespective energy states and transitions of energy states, and whereinthe determining operation includes determining whether the in situvalues associated with any one or more of the respective energy statesor transitions of energy states deviates from a corresponding referencevalue associated with the particular respective energy state ortransition of energy state.